Electrical connector

ABSTRACT

In this electrical connector, an electrical connection is made through a low melting point alloy consisting essentially of gallium and indium which is liquid at room temperature. In order to retain the low melting point alloy, contact points may be made of a porous solid material impregnated with the low melting point alloy, or may be made of cadmium, bismuth or lead having interfaces between which the low melting alloy is precipitated. In any case, gallium may be provided at one contact point and indium at the other contact point, so that when the two points are brought together the low melting point alloy is formed.

United States Patent lnventors Takai'ie Tsuchiya Appl. No.

Filed Patented Assignee Priorities [50] Field of Search 339/1 l8.Yokohama-shi; 275, 278; 29/ l 94, I99 Tetsuya Ohtani, Yokohami-shi;Akira Sato, Tokyo; Syoichi Ito, Yokohama-shi, all of [56] ReferencesCited Japan UNITED STATES PATENTS 332,456 3,023,393 2/l962 Oliver 339/]18 D91!- 1969 3,184,303 5/1965 Grobin 75/ l 34 Nov. 23, 1971 Tokai DenkiKabushiki Kaisha Primary Exammer.loseph McGlynn Tokyo, JapanAttorney-Marshall & Yeasting Aug. 5, 1969 122 2 ABSTRACT: In thiselectrical connector, an electrical connection is made through a lowmelting point alloy consisting essentially of gallium and indium whichis liquid at room temperature. In order to retain the low melting pointalloy, contact points may be made of a porous solid material im- Aug. 7,1969, Japan, No. 44/621116 ELECTRICAL CONNECTOR pregnated with the lowmelting point alloy, or may be made of 6 Claims, 14 Drawing Figs.

cadmium, bismuth or lead having interfaces between which US. Cl 339/118R, the low melting alloy is precipitated. in any case, gallium may339/275 339/278 C be provided at one contact point and indium at theother conlnt. Cl H0lr 3/08 tact point, so h h th t o points are broughttogether the low melting point alloy is formed.

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26 27 i g z ELECTRICAL CONNECTOR BACKGROUND OF THE INVENTION Thisinvention relates to an electrical connector which can be used forconnecting electrical conductors in various types of electricalapparatus, such as communication equipment, electrical machinery andother electrical equipment.

In the known electrical connectors, it is conventional to form anelectrical connection by holding contact surfaces together underpressure.

In such known electrical connectors, the contacting surfaces aregradually corroded or contaminated by the action of the atmosphere, sothat the electrical resistance across the connection graduallyincreases. Under such conditions, the minimum force with which thecontacting surfaces must be held together in order to provide a certainminimum resistance across the connection gradually increases. Because ofthe modern tendency toward miniaturization of electrical apparatus, thecontact pressure which can be provided is limited, so that it is notpossible to employ high contact pressure in order to maintain thedesired low resistance across a pair of contacts.

SUMMARY OF THE INVENTION The present invention overcomes these and otherdisadvantages of the known connectors and affords addition advantages.In an electrical connector embodying the present invention, anelectrical connection is made through a low melting point alloyconsisting essentially of gallium and indium which is a liquid at roomtemperature. The preferred alloy is a eutectic alloy of gallium andindium.

A primary object of the invention is to provide a low contact resistanceby forming an electrical connection through an alloy which is a liquidat room temperature, consisting essentially of gallium and indium, whichis present on the contacting surfaces.

A secondary object of the invention is to prevent the gradual increasewhich takes place in the resistance of the known connectors, so thathigh contact pressure is not required.

Other objects of the invention are to eliminate the need for periodiccleaning of contacts, to eliminate the need for appreciable contactpressures, and to make it possible to produce perfect and permanentelectrical connections by mere assembly without the use of complicatedoperations such as soldering. A permanent, solid connection may beachieved in the practice of the present invention, by providing, incontact with the indium-gallium alloy which is a liquid at roomtemperature, a metal which diffuses there into and thereby converts thelow melting point alloy into a solid alloy. Such conversion of thenormally liquid alloy into a solid alloy is a gradual process, so thatthe electrical connection may be repeatedly broken and remade duringassembly, and the connection does not solidify until sometime after allassembly operations are completed.

Thus the present invention saves labor and makes possible moreeconomical manufacturing methods, in addition to providing a moredependable and lasting electrical connectron.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side elevation of aconventional electrical connector in its assembled state.

FIG. 2 is a side elevation of a preferred form of electrical connectorembodying the invention, showing its appearance prior to assembly of theconnector.

FIG. 3 is a side elevation of the electrical connector of FIG. 2 in itsassembled state.

FIG. 4 is a longitudinal section of another connector embodying theinvention.

FIG. 5 is a similar section showing the elements of FIG. 4 beforeassembly.

FIG. 6 is a longitudinal section of a third form of connector embodyingthe invention.

FIG. 7 is a section similar to FIG. 6, showing the elements of theconnector before assembly.

FIG. 8 is a perspective view of a terminal block embodying theinvention.

FIG. 9 is a perspective view of bodying the invention. I

FIG. 10 is a longitudinal section of another connector embodying theinvention, showing the parts before assembly.

FIG. 11(A) is a fragmentary diagrammatic view showing the parts of theconnector of FIG. 10 assembled to form a temporary connection.

FIG. 11(8) is a fragmentary diagrammatic view showing the parts of theconnector ofFIG. 10 in their final assembled condition.

FIG. 12 is a longitudinal section of another connector embodying theinvention, showing the parts before assembly.

FIG. l3( A) is a fragmentary diagrammatic view showing the parts of theconnector of FIG. 12 partially assembled.

FIG. 13(8) is a fragmentary diagrammatic view showing the parts of theconnector of FIG. 12 in their final assembled condition.

FIG. 14 is a diagrammatic view of bodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a conventionalelectrical connector, in which the two contacts consist of a plug 1fixed in a holder of suitable insulating material and a jack 3,3 fixedin another holder 4 of insulating material. The jack 3,3 is resilient,so that when the plug is inserted into the jack a certain amount offorce must be used, and the assembled contacts are then held togetherunder sufficient pressure to provide the necessary low resistance acrossthe connector. A disadvantage of this connector is that the resistancegradually increases because of the action of the atmosphere in corrodingor contaminating the connecting surfaces, and the accumulation of dustand dirt upon the contacting surfaces.

In order that the connector may form part of an electrical circuit,connecting members such as the plug 1 and the jack 3,3 are permanentlyconnected to wire leads 5,5.

The low melting alloy used in the practice of the present invention isan alloy consisting essentially of gallium and indium. When gallium iscontacted with indium, a liquid alloy is formed at a temperature as lowas C. If the indium contains zinc or tin, a liquid alloy may be producedby contacting it with gallium at a temperature as low as 9 C.

In the connector embodying the invention shown in FIG. 2, gallium or aeutectic alloy ofgallium is applied at 6 to the contact portion of theplug 1, and indium or a eutectic alloy of indium is applied at 7 on thesurface of the jack 3,3 which is contacted when the plug 1 is inserted.

As shown in FIG. 3, when the plug 1 is inserted into the jack 3,3, aliquid alloy 6,7 of gallium and indium is formed, and this liquid alloyforms a junction between the contacting surfaces of the plug and thejack.

In a connector embodying the invention, such as that shown in FIG. 3,substantial pressure is not required to form a connection of lowresistance, and mere contact between the connecting members which areseparated by the liquid alloy is sufficient to provide a contact orelectrical connection of low resistance The quantity of the liquid alloywhich is required in a connector embodying the invention is very small,and the liquid alloy is maintained on the contact surfaces by adhesionand cohesion. In a connector embodying the invention, the electricalconnection is not impaired by vibration or shock, because the connectingmembers are electrically joined by the liquid alloy. Moreover, in aconnector embodying the invention there is no danger that the resistancemay be increased by the action of gases in the atmosphere or byaccumulation of dust or dirt.

In a connector embodying the invention, the connecting members, whichare usually made of copper, may be plated another terminal block emafurther connector emwith chromium or titanium. The diffusion of chromiumor titanium into a liquid alloy of gallium and indium is very slow sothat the liquid fonn of the alloy is preserved for a very extendedperiod of time when the connecting members are plated with chromium ortitanium.

An automatic telephone exchange usually is assembled from a large numberof panels or shelves. When these panels are mounted in place, it isnecessary to make wire connections between the shelves and the wiringoperation is very tedious. In order to expedite the work of wiring thepanels in an automatic telephone exchange, attempts to use electricalconnectors have been made, but is has been found that electricalconnectors which can be provided upon the panels are not reliable.

When the connector shown in FIGS. 2 and 3 is to be used on panels for anautomatic telephone exchange, excellent and reliable results can beobtained by making the plug and jack of phosphorous bronze, galvanizedwith silver or gold. Gallium is applied to the plug at 6, and indium ora eutectic alloy of indium is applied to the jack at 7. In the connectorshown in FIG. 2, the gallium at 6 and the indium at 7 are solidmaterials before the plug is inserted into the jack. As soon as the plugis inserted, a liquid alloy is formed from the gallium and indiumbetween the contacting surfaces of the plug and jack. Gold, silver orcopper surfaces on the plug or jack, when in contact with the liquidgallium-indium alloy, diffuse into the liquid alloy and thus graduallyconvert the liquid alloy into a solid by raising the melting point ofthe alloy. However, the resulting solid alloy is relatively soft so thatthe plug can be pulled out of the jack without difficulty, particularlywhen the connector is warm.

In the connector shown in FIGS. 4 and 5, a plug is formed by a holder 8of insulating material carrying a resilient contact member 9. A jack isformed of a holder 10 of insulating material provided with a contactmember 11 adapted to extend adjacent to the contact member 9. Thecontact member 11 does not need to be resilient. Lead wires 12 areconnected to the contact members 9 and II. A cylindrical receptacle 13,made of elastic material, is open at the top and contains a low meltingpoint alloy 14 which is a liquid at room temperature and consistsessentially of gallium and indium. The alloy 14 is covered with a thinfilm A, which is made of paraffin, rubber, a plastic material or thelike, and which retains the low melting point alloy 14. The contactmembers 9 and 11 may be made of copper or a copper alloy, and thecontact portions 9 and 11 of these contact members may be left bare ormay be galvanized with gold or silver. When the receptacle 13 isinserted in place as shown in FIG. 4, the contact portions 9' and I1puncture the film A and are then surrounded with the galliumindium alloyin the receptacle, which wets the contact portions 9' and 11' and fonnsthe electrical connection between them. The alloy forms a perfectelectrical connection which does not depend upon pressure between thecontact members. If the contact portions 9' and 11' have been platedwith titanium or chromium, or are made of stainless steel, the alloywill remain liquid at room temperature for an extended period of time.On the other hand, if the surfaces of the contact portions 9 and l 1consist of copper, a copper alloy, gold, silver or the like, gradualdiffusion of the metal from the surfaces of the contact portions 9' and11' into the gallium-indium alloy occurs to produce a eutectic alloywhich has a melting point above room temperature, so that a solidconnection between the contact portions 9' and I1 is formed after aperiod of time.

The embodiment shown in FIGS. 4 and 5 is useful in fonning a permanentconnection as distinguished from a connection which is frequently brokenand remade, for example, in wiring a panel. An electrical connectionformed in this manner does not deteriorate with age, and a permanentconnection is formed which may gradually increase in strength bydiffusion of metal into the gallium-indium alloy.

In the embodiment shown in FIGS. 6 and 7, the contact portions 9 and IIare initially coated with indium or an indium alloy, while the fillingin the receptacle I3 is gallium or a gallium alloy covered with the filmA. Alternatively. the coating 14a on the contact portions 9' and II mayconsist of gallium or a gallium alloy, if the filling 14b in thereceptacle 13 consists of indium or an indium alloy. In either case, thecoating 14a and the filling 14b consist of solid materials. X

When the parts are assembled as shown in FIG. 6, the indium and galliumcome into contact, thus forming an alloy having a melting point belowroom temperature which is normally liquid.

Except as described above, the connector illustrated in FIGS. 6 and 7functions like the connector illustrated in FIGS. 4 and 5.

FIG. 8 shows how the invention may be embodied in a terminal bar havingterminals to be connected with lead wires. In this embodiment, a groupof tenninals 15 are to be permanently connected to lead wires. Theterminals 15 are mounted upon a tenninal bar 16 of insulating material.The receptacle 17 is similar to the receptacle 13 of FIGS. 4 and 5, andis filled with a gallium-indium alloy covered with a film A.

The lead wire 19 is placed with its end extending into a notch 15a in aterminal 15, and the receptacle 17 is then telescoped over the terminal15 so that the terminal I5 and the lead wire 19 become embedded in theliquid alloy 18. The indium-gallium alloy then wets the wire 19 and theterminal 15, to complete an electrical connection between them.

The embodiment of FIG. 9 differs from the embodiment of FIG. 8 in thatinitially the gallium or gallium alloy is separate from the indium orindium alloy, one of these materials being contained in a coating 18a oneach of the terminals 15, and

' the other of these materials constituting a filling 18b in each of thereceptacles '17, covered with a film A. When the embodiment shown inFIG. 9 is assembled as described in connection with the embodiment ofFIG. 8, a gallium-indium alloy is formed in each of the receptacles 17which is a liquid at room temperature. This liquid alloy may begradually converted into a solid alloy by diffusion of the metalconstituting the terminal 15.

The embodiments shown in FIGS. 10 to 14 are designed to protect againstescape of the liquid alloy. For this purpose, the gallium which is to beconverted into a liquid alloy by contacting it with indium may bepresent as a precipitate in the inter faces of a body of cadmium,bismuth or lead. Also, the gallium or the liquid alloy itself may bepresent as an impregnant in a porous body made of glass or a plastic, ormade of a metal powder by powder metallurgy techniques. Theseembodiments are useful not only for retaining the liquid alloy, but alsofor retaining gallium in cases in which the melting point of gallium (30C.) may be exceeded.

A solution of gallium in cadmium, bismuth or lead, containing from 10 to20 percent of gallium be weight, can be produced by heating to severalhundred degrees C. Upon coding, such a solution of gallium becomessupersaturated, and when the solidified material is held at a reducedtemperature, particles of gallium precipitate at the interfaces betweenthe crystals of cadmium, bismuth or lead. The size of the galliumparticles can be increased by heat treatment. In the resulting system,the gallium is effectively retained and does not escape even when thematerial is heated above 30 C. When the surface of such a material,having gallium precipitated at the interfaces, is brought into contactwith a surface containing indium, a liquid alloy of gallium and indiumis produced which forms a good electrical connection by wetting thecontacting surfaces.

Gallium or a gallium-indium alloy also may be retained and protectedagainst escape by incorporating it in a porous material as animpregnant. If the porous material is made by powder metallurgytechniques, it should be produced by use of a metal powder of titanium,chromium, tungsten, or another metal which is inert to gallium. Thediameter of the pores in such a porous material may be about 50 microns.

The impregnation of the porous material may be carried out by heatingthe material in a vacuum and then exposing it to gallium vapor, ifdesired while subjecting the material to ultrasonic vibration.

Contacts employing the system just described preferably are notsubjected to repeated making and breaking. and preferably are used asstatic or permanent contacts. FIG. and 11 show an embodiment in whichordinary metal-to-metal contacts are provided for temporary use duringtrials and testing and the gallium-indium alloy connection of thepresent invention is effected during final assembly of the apparatusafter all preliminary tests and checks have been performed.

In FIG. 10 the holder of insulating material contains a resilient plate22 having its end bent in the shape of an inverted U, and a secondresilient plate 21 having a hooked end 21a and a slot 21c. A boxlikespace is provided between the bent portion 22a of the member 22 and thehooked portion 21a of the contact member 21. The boxlike space 23 isused to hold a connecting body 24 consisting of cadmium, bismuth or leadhaving gallium precipitated in the interfaces. The resilient member 22acts as a keeper, holding the body 24 against the slot 21c. The contactmember 21 and the keeper member 22 preferably are plated with nickel,chromium, titanium, or another metal which does not appreciably diffuseinto a gallium-indium alloy.

A plug is formed by a holder 25 of insulating material carrying acontact prong 26 for engaging the contact member 21. On the uppersurface of the contact prong 26 is provided a connecting surfaceconsisting of indium or an indium alloy. Lead wires 28 are connected tothe contact member 21 and the contact prong 26.

FIGS. 1 IA and 11B illustrate the operation of the connector shown inFIG. 10.

FIG. 11A shows a condition in which the prong 26 is only partiallyinserted, in order to make a temporary electrical connection withoutbringing the indium surface 27 in contact with the gallium-containingmaterial 24. In the condition, the electrical connection is bymetal-to-metal contact. This is a "primary contact state in which noliquid alloy is formed. Such partial insertion of the prong 26 isemployed during trial assembly, for testing and checking when repeatedmaking and breaking of the connection may occur. After all connectionshave been checked and found to be correct, the final connection isformed by pressing the parts fully together to insert the "prong 26completely as shown in FIG. 1 1B. When this is done,

the indium-containing material 27 is brought into contact with thegallium-containing material 24 so that a liquid alloy of indium andgallium is formed between the contacting surfaces. This connection isformed through the slot 21c, into which the indium-containing body 27projects to contact the galliumcontaining body 24.

It will be understood that the prong 26 is wider than the slot 210, sothat the prong 26 slides under the comer 21b of the contact member 2]and does not enter the slot 210.

In the modification shown in FIG. 12, the contact member 21 and theprong 26 are both provided with a coating of an indium-containingmaterial 29. Upon assembly of the elements shown in F IO. 12, asillustrated in FIG. 13A, a temporary electrical connection is madebetween the indium-containing surfaces 29. When a permanent connectionis to be effected, it is necessary to interpose a holder 31 ofinsulating material which may cooperate with a series of alignedconnectors of the type shown in FIG. 12. The holder 31 has a series ofholes, each of which is filled with a connecting material 30 consistingof cadmium, bismuth or lead containing gallium precipitated at theinterfaces. The holder 31 is inserted in proper alignment with a seriesof connectors so that a body of connecting material 30 in one of theholes is brought between the indium-containing surfaces 29 of eachconnector. In this way, a permanent connection is produced by formingsome of the liquid alloy on both of the indium-containing surfaces 29 ofeach connector.

In the embodiment shown in FIG.14, the contact members 32 and 33 areprovided with contact points 32a and 330 each of which consists of abody of porous metal impregnated with a liquid alloy of gallium andindium. The contact points 32a and 33a perform well with repeated makingand breaking,

because the liquid alloy in the pores of the porous metal forms a liquidconnection when the contact points 32a and 33a are brought together.Whenever these contact points are separated, the liquid alloy isretained in the pores of the porous metal by capillarity.

In the practice of the present invention, an electrical connection ismade through an alloy consisting essentially of gallium and indium whichis a liquid at room temperature. When the electrical connection is thusformed by a liquid alloy, the resistance across the connector is stableand does not vary with contact pressure or increase upon exposure to theatmosphere.

The liquid alloy consisting essentially of gallium and indium which isused in the practice of the present invention is superior to mercury inthat it does not emit a toxic vapor.

We claim:

1. An electrical connector comprising two members which are adapted tobe assembled to form an electrical connection, each member having anelectrically conducting element which extends adjacent to anelectrically conducting element of the other member, and a body of a lowmelting point alloy consisting essentially of gallium and indium whichis a liquid at room temperature, forming a junction between the twoelements.

2. An electrical connector according to claim 1 comprising, in contactwith the low melting point alloy, a metal which diffuses thereinto andthereby converts the low melting point alloy into a solid alloy.

3. An electrical connector according to claim I wherein each member hasan electrically conducting contact which is directly engageable by anelectrically conducting contact of the other member to form a temporaryconnection, and an electrically conducting element which is adapted tobe interposed between the two contacts to form a permanent electricalconnection between the two contacts through a body of a lowmelting-point alloy consisting essentially of gallium and indium whichis a liquid at room temperature.

4. An electrical connector according to claim I wherein an electricalconnection is made through a porous solid material impregnated with thelow melting point alloy.

5. An electrical connector according to claim 1 comprising a connectingmember having a surface comprising indium, and a second connectingmember having a surface which comprises gallium and is engageable withthe surface comprising indium to form an alloy therewith.

6. An electrical connector according to claim 5 wherein the secondconnecting member has a surface comprising a material of the classconsisting of cadmium, bismuth and lead having interfaces between whichgallium is precipitated.

1. An electrical connector comprising two members which are adapted tobe assembled to form an electrical connection, each member having anelectrically conducting element which extends adjacent to anelectrically conducting element of the other member, and a body of a lowmelting point alloy consisting essentially of gallium and indium whichis a liquid at room temperature, forming a junction between the twoelements.
 2. An electrical connector according to claim 1 comprising, incontact with the low melting point alloy, a metal which diffusesthereinto and thereby converts the low melting point alloy into a solidalloy.
 3. An electrical connector according to claim 1 wherein eachmember has an electrically conducting contact which is directlyengageable by an electrically conducting contact of the other member toform a temporary connection, and an electrically conducting elementwhich is adapted to be interposed between the two contacts to form apermanent electrical connection between the two contacts through a bodyof a low melting point alloy consisting essentially of gallium andindium which is a liquid at room temperature.
 4. An electrical connectoraccording to claim 1 wherein an electrical connection is made through aporous solid material impregnated with the low melting point alloy. 5.An electrical connector accordIng to claim 1 comprising a connectingmember having a surface comprising indium, and a second connectingmember having a surface which comprises gallium and is engageable withthe surface comprising indium to form an alloy therewith.
 6. Anelectrical connector according to claim 5 wherein the second connectingmember has a surface comprising a material of the class consisting ofcadmium, bismuth and lead having interfaces between which gallium isprecipitated.